I have a 2002 A6 4.2 that came with the 17"x8" wheels with 35 mm offset. The tires are 255/40 x17".
I decided to replace the wheels and bought some 18"x8" with 35MM offset. When I called TireRack about tires they said that 255/35 tires require a 8.5" rim and that they couldn't recommend a tire for this set up. In fact they said they wouldn't recommend that wheel and that I should have purchased 18"x8.5" rims. I called the wheel supplier (OEWheelsllc) and they said that a 245/35 x18" should fit, no problem.
Any comments or suggestions? I am considering canceling the order and sticking with my stock rims.

 

255's on a 8" rim will leave a lot of tire hanging since they're too wide for the wheel. 235's on a 8" rim are just right. 245's on a 8.5 so on....


And you can be running 8" no problem. But I don't understand why someone would get 255/40/17, that's a stupid configuration

 

255/40 17 are the stock size for that wheel. That's how Audi equipped them.

 

I have 235/40/18 inch tires on 18 X 8.5 inch rims. I have to use 5mm spacers for the 35mm offset.